ditch awaits in docker compose file

from [`docker-compose.yml`](https://github.com/confluentinc/kafka-streams-examples/blob/master/docker-compose.yml#L112-L126):
> TODO: Once https://issues.apache.org/jira/browse/KAFKA-5037 is resolved, we can remove this `command` and use the image as-is.
Now, at this point [`KAFKA-5037`](https://issues.apache.org/jira/browse/KAFKA-5037) does appear marked as `RESOLVED`. :smile:
